1. Field of the Invention
The present invention is generally related to a torque transmitting device for a marine propulsion system and, more particularly, to a device for allowing relatively significant twist to occur between the propeller shaft and the propeller hub at relatively low torque transfer magnitudes up to a preselected magnitude of twist, after which the torque transmitted as a function of relative twist (i.e. inch-pound per degree) increases significantly.
2. Description of the Prior Art
Many different types of mechanisms are known to those skilled in the art for the purpose of attaching a propeller to a propeller shaft.
U.S. Pat. No. 5,201,679 which issued to Velte et al on Apr. 13, 1993, describes a marine propeller with a breakaway hub. The marine propeller has an insert cavity with pentagonal cross section extending coaxially with the axis of rotation of the propeller, along with at least a portion of the length of the propeller. A resilient insert corresponding to the insert cavity is positioned in the insert cavity. The insert is sized for slip fit with the cavity and is adapted for connection with a propeller driveshaft. Preferably, the insert has a cylindrical aperture with a series of grooves disposed circumferentially thereabout extending coaxially through the inset and the insert is connected with the propeller shaft through a shaft sleeve. The shaft sleeve corresponds to the aperture in the insert, has a cylindrical outer surface with a series of teeth disposed circumferentially thereabout, and has a mounting aperture extending coaxially through the shaft sleeve. The shaft is sized for hand force slip fit engagement with the insert. The mounting aperture is adapted for mounting the marine propeller on the propeller shaft.
U.S. Pat. No. 3,748,061, which issued to Henrich on Jul. 24, 1973, describes a propeller construction in which a propeller includes a bushing part adapted to be mounted on a propeller shaft for common rotary movement of the bushing part with the propeller shaft. A resilient member is bonded to the outer periphery of the bushing and has an outer non-circular configuration including a series of alternate areas of greater and lesser radial distance form the axis of said bushing and a propeller blade part has a hub including a bore with an inner configuration including a series of alternate areas of greater and lesser radial distance from the axis of the propeller and detachably receiving the resilient member.
U.S. Pat. No. 5,244,348, which issued to Karls et al on Sep. 14, 1993, discloses a propeller drive sleeve. A shock absorbing drive sleeve is provided by a molded plastic member directly mounting the propeller hub to the propeller shaft. The sleeve has a rearward inner diameter portion engaging the propeller shaft in splined relation, and a forward inner diameter portion spaced radially outwardly of and disengaged from the propeller shaft. The drive sleeve has a rearward outer diameter portion, and a forward outer diameter portion engaging the propeller hub. The drive sleeve and the propeller hub are tapered relative to each other such that a forward outer diameter portion of the drive sleeve snugly engages the propeller hub, and a rearward outer diameter portion is spaced slightly radially inwardly of the hub by a small gap and may partially rotate relative to the propeller hub in response to rotation of the propeller shaft drivingly engaging the rearward inner diameter portion. When the propeller strikes an object, the shock is absorbed by torsional twisting of the drive sleeve wherein the rearward inner diameter portion and the rearward outer diameter portion continue to rotate to a further rotated position than the forward outer diameter portion, whereafter the splined teeth of the rearward inner diameter portion shear.
U.S. Pat. No. 4,701,151, which issued to Uehara on Oct. 20, 1987, describes a propeller damping arrangement for a marine propulsion device. A number of embodiments of coupling arrangements for coupling a propeller to a driving shaft that permit a higher degree of resilience in a circumferential direction than in an axial direction are disclosed. As a result, the coupling may be designed so as to offer high degree of vibration damping while affording good resistance to axial driving thrust. In addition, each embodiment is designed so as to provide more resilience in the reverse drive condition than in the forward drive condition.
U.S. Pat. No. 4,642,057, which issued to Frazzell et al on Feb. 10, 1987, discloses a shock absorbing propeller. A marine propeller mounting arrangement includes a sleeve member for mounting on a propeller shaft, a propeller having an inner hub which fits over the sleeve member and a cushion member fitting between the sleeve member and the propeller inner hub. The sleeve member includes radially extending projections registering the channels in the hub to positively drive the propeller, even in the event of failure of the cushion member. The propeller has an outer hub surrounding the inner hub to define an exhaust gas passageway through the propeller.
U.S. Pat. No. 4,566,855, which issued to Costabile et al on Jan. 28, 1986, describes a shock absorbing clutch assembly for a marine propeller. The propeller hub as an axial hole therein having a wavy, non-cylindrical surface consisting of a plurality of alternating peaks and valleys. A closely fitting resilient insert slips into the axial hub hole of the propeller hub and has an outer surface with peaks that extend into the respective valleys of the axial hub hole. The resilient insert has a cylindrical axial hole therein with a plurality of longitudinal keyways disposed in the surface of that hole. The keyways receive respective keys rigidly attached to the outer spline of a spline driver adapter sleeve, the inner surface of which has keyways that receive the splines of a driveshaft of a marine motor. The resilient insert transfers torque from the driving shaft to the hub without slippage of the torque is less than a predetermined amount, and absorbs shock if the propeller strikes a rock or the like by allowing the peaks of the hub hole to compress the peaks of the resilient insert. The resilient insert allows slipping of the hub relative to the driving shaft if the torque on the driveshaft exceeds a predetermined amount of torque.
U.S. Pat. No. 5,322,416, which issued to Karls et al on Jun. 21, 1994, discloses a torsionally twisting propeller drive sleeve. In a marine drive, a drive sleeve between the propeller shaft and the propeller hub absorbs shock after the propeller strikes an object by torsionally twisting between a forward end keyed to the propeller hub and a rearward end keyed to the propeller shaft. The drive sleeve is composed of a plastic material providing torsional twisting angular rotation at a first spring rate less than 100 lb. ft. per degree from 0xc2x0 to 5xc2x0 rotation, a second higher spring rate beyond 5xc2x0 rotation, and supporting over 1,000 lb. ft. torque before failure.
The patents described above are hereby expressly incorporated by reference in the description of the preferred embodiment.
As can be seen in the descriptions of the prior art, as shown above, many different types of resilient inserts have been developed to connect a propeller hub to a propeller shaft and to achieve various desired advantages. One problem that is common in many different types of marine propulsion systems is the noise generally referred to as xe2x80x9cprop rattlexe2x80x9d. This rattle actually occurs in the drive train and can be caused by the provision of a varying magnitude of torque at the propeller shaft. Since the propeller shaft and driveshaft of a marine propulsion device typically receive torque from an internal combustion engine, the sequential firing (i.e. igniting of the fuel/air mixture) within the combustion chambers of the engine creates individual pulses of downward force on the associated pistons. These individual downward forces transmit torque to the crankshaft of the engine as distinct pulses. These distinct pulses of torque are transmitted through the interconnection of the crankshaft to the driveshaft and, in turn, to the propeller shaft. Therefore, the torque provided at the propeller shaft is not constant over time but, instead, comprises a plurality of distinctive peaks of torque that are generally coincident with the downward movement of the various pistons of the internal combustion engine.
Since the rotating propeller hub and blades attached to the propeller shaft have a certain degree of inertia, the intermittent torque peaks described above create a situation in which the propeller shaft and the propeller hub oscillate angularly relative to each other. In other words, when the propeller shaft experiences a torque peak as a piston transmits torque to the crankshaft, the propeller shaft rotates relative to the propeller hub in a first direction. Then, as the propeller hub reacts to this torque peak at a slightly later time, the propeller hub rotates at a higher angular velocity than the propeller shaft and the relative angular positions of the propeller shaft and the propeller hub move to an opposite direction. As a result, under certain circumstances, the propeller hub and the propeller shaft continually oscillate relative to each other about their common central axis. This oscillation can result in relative angular reversals of various components in the power transmission system which includes the propeller shaft, the clutch, the bevel gear, the driveshaft, and the crankshaft of the engine. This relative oscillation between components create the audible xe2x80x9cprop rattlexe2x80x9d that can diminish the enjoyment of operating a marine vessel.
In view of the above discussion, it can be seen that it would be significantly beneficial if a torque transmitting component could be provided that allows significant relative rotation between the propeller hub and the propeller shaft at relatively low magnitudes of torque transfer between those components up to a significant angular displacement between the propeller shaft and propeller hub. Correspondingly, it would also be significantly beneficial if this type of torque transmitting component could also transmit significant magnitudes of torque when the relative rotation between the propeller hub and propeller shaft increase beyond a relatively high magnitude of twist. As a result, xe2x80x9cprop rattlexe2x80x9d would be significantly reduced or eliminating when the engine is operating at idle speed with small amounts of torque being transmitted between the propeller shaft and propeller hub, but with the provision that at higher relative twists between the propeller shaft and propeller hub large magnitudes of torque can be provided when the associated marine vessel is operated at higher speeds.
A torque transmitting device for a marine propulsion system made in accordance with the present invention comprises an adapter that is shaped to be attached in torque transmitting relation with a propulsor shaft of the marine propulsion system. The propulsor shaft is rotatable about a central axis of rotation. The propulsor shaft can be either a propeller shaft or a shaft for an impeller. A first insert portion is shaped to be attached in torque transmitting relation with the adapter and a second insert portion is shaped to be attached in torque transmitting relation with a propulsor hub. The propulsor hub can be the hub of either a propeller or impeller. A third insert portion is connected between the first and second insert portions and is resilient in order to allow the first and second insert portions to rotate relative to each other about the central axis of rotation of the propulsor shaft. The adapter is shaped and proportioned relative to the other components of the present invention to prevent the first, second, and third insert portions from being compressed in a direction parallel to the central axis of rotation when the adapter is attached to the propulsor shaft.
In a particularly preferred embodiment of the present invention, the adapter comprises an inner opening which has a first plurality of axially extending ridges shaped to mesh with a second plurality of axially extending ridges formed on an outer surface of the propulsor shaft. In other words, the adapter has an inner opening that has spline teeth that can mate in meshing relation with spline teeth on the propulsor shaft. The adapter is disposable in coaxial relation with the propulsor shaft about the central axis of rotation, whereby rotation of the propulsor shaft causes synchronous rotation of the adapter. In certain embodiments of the present invention, the adapter comprises an outer surface having a first discontinuity formed therein by ridges, said first insert portion comprising an inner surface having a second discontinuity formed therein by grooves, with the first and second discontinuities. being shaped to attach the first insert portion to the adapter for rotation in synchrony with the adapter. In a preferred embodiment of the present invention, a second insert portion comprises an inner surface having a third discontinuity formed therein by grooves, with the first and third discontinuities being shaped to attach the second insert portion to the adapter in a manner which permits a first predetermined magnitude of relative rotation between the adapter and the second insert portion. The first predetermined magnitude of relative rotation is provided by a first space between the first and second discontinuities which allows lost motion to occur between the second insert portion and the adapter.
In a preferred embodiment of the present invention, the second insert portion comprises an outer surface that is shaped to be received by the propulsor hub and attach the second insert portion to the propulsor hub for rotation in synchrony with the hub. The first insert portion comprises an outer surface that is shaped to be received within the second propulsor hub in order to attach the first insert portion to the propulsor hub for rotation in a manner which permits a second predetermined magnitude of relative rotation between the first insert portion and the propulsor hub. The second predetermined magnitude of relative rotation is provided by a second space between the outer surface of the first insert portion and an inner surface of the propulsor hub which allows lost motion to occur between the first insert portion and the propulsor hub.
The third insert portion, in a preferred embodiment of the present invention, is sufficiently resilient to allow a third predetermined magnitude of relative rotation to occur between the first and second insert portions. The third insert portion can comprise a plurality of metal rods that are attached between the first and second insert portions. The metal rods can be titanium. It should be understood that nonmetallic rods can also be used. In a preferred embodiment of the present invention, the first, second, and third insert portions are separable components, wherein the first and second insert portions are each removably attached to the third insert portion.